HVLP tip sizes and air source conditioners

Also, I have an accuspray 10 series siphon gun and was looking at some gravity feed, reduced pressure guns that run on shop air for top coating. I was thinking of setting up the accuspray for primer, surfacer, (new tips and nozzles, if necessary) and getting a new upper end gravity feed gun for the finish. What filters, air line driers, etc, should I use to make sure I get good clean air? Any reccomendations?

Thank You,

scott#2

Here's my take on the issue of tip size:

The tip size you use has to do with the type of feed your gun has, the viscosity of the material being sprayed and the desired paint application rate (oz/min). In general, for the same viscosity and the same application rate, a siphon feed gun will require a larger tip than a gravity feed gun. Under the same conditions, a pressure feed gun will require the smallest tip size.

For example, the standard stock tip size for a siphon feed, full-sized gun is a 1.8mm that flows up to 12 oz/min. For a gravity feed gun, it's more like a 1.5mm tip and for a pressure feed arrangement, it's more like 1.1mm. These tip sizes should flow most common automotive type painting materials. The line between choosing one tip size over the other is not hard and fast. There is a broad overlap where a smaller or larger tip size can be used with a material of the same viscosity. With the same gun and same material, going up one tip size will increase the paint flow and hence the application rate. For the same pattern size (e.g. 8"), that will result in a "faster" gun where you have to increase the speed of your pass movement. That assumes, of course, that your air cap has sufficient capacity to properly atomize the higher paint flow. In order to keep the same application rate with a more viscous material, you can also use a larger tip. This is why many surfacers (higher viscosity) typically will indicate that a larger tip size is recommended. Use of a smaller tip will still work but the application rate will be reduced and the pattern size and atomization may be affected. It's not that big a deal with a surfacer because that's going to be sanded anyway.

Click on the thumbnail below to get a readable view from a page in "The ABCs of Spray Finishing" by DeVilbiss. The document is pretty generic in nature and I think it can be applied to most spray guns from other manufacturers. I do think there is a typo in the application rates for gravity-fed non-hvlp tip sizes. Those seem too high to me. The others seem about right. You can download the entire pdf document (caution - 1.5MB) here.

For Marlin: Proper understanding and setting of the air pressure is extremely important in order to get a good application from any gun. You can compensate a bit for having too large a tip size for the material used buy choking down on the fluid needle in order to basically decrease the paint orifice area. Generally, however, you keep the fluid and air adjustment screws on the gun at near full open. You can also speed up your pass movement to compensate for a tip on the large side. The air adjustment screw is for changing the pattern size not for adjusting the atomization pressure. You need to obtain the necessary air pressure (dynamically) measured at the air inlet to the gun in order to get the best performance. The way to do this is explained here.

Rod

The systems that Marlin and I are using, use a little "turbin" fan box that puts out a very high volume of warm, dry air. Its much like the output of a vacume cleaner. (blower side) except very high volume air. There is no compressing of the air, so typically you dont have to worry about filters and line driers. I am sure you have seen these rigs before but wether you have used one or not Im not sure, kind of a poor mans spray rig, although they are quite expensive. When these turbine units come into play, all HVLP guns aren't created equal. I was ready to buy a decent gravity feed HVLP gun the other day and the guy said that I have to use low pressure shop air to run it and then get filters and driers and the like. I would still like to do that because I here you get a much better finish with these shop air HVLP guns. I used an Accuspray series 10 bleeder gun and the turbine on the last tractor I painted and the results were good, but not as good as I have seen in my buddies body shop where he uses shop air HVLP, thats why the curiosity.

I guess what Im trying to say here is that, you cant use any of the higher end HVLP guns on these turbine systems, they are a different animal all together. That being said, I am still curious if the tip, nozzle, air cap parameters spelled out in your post still apply to these "turbine style" guns?

99% of all the better HVLP guns made by Sata, Devillbis, Sharpe, and whoever else are designed to be used on shop air. Accupsray does make 1 gravity feed gun for the turbine system but I am starting to shy away from it and I am looking at DeVilbiss, Sata, Sharpe, etc. I would like to get a shop air spray system set up with filters, etc. for other work I get into. Any recomendations on guns, filter types, driers, etc?

scott#2

Sorry about that. I completely misunderstood the matter. I guess I just keyed in on Marlin calling his unit a "compressor-driven gun". Forget everything I said. I know nothing about turbine driven guns. You are correct. The turbine type guns are very different animals. I doubt that anything in the DeVilbiss literature applies. The only thing I can suggest is to refer to the instructions that came with such equipment for any details regarding tip sizes, adjustments, etc.

Thanks for bringing that huge error to my attention. Maybe someone who is familiar with that type of spraygun can provide some input.

Guns, filters, driers. Gee, each one is a subject in itself. The quick answer on guns is any of the major manufacturers. Mine are DeVilbiss but that doesn't mean that the other well known brands are inferior in any way. Sharpe has a reputation for good quality at a reasonable price. Don't count on filters to solve a moisture problem. Filters are for removing particulates, not water. Metallic piping runs that cool the air and condense out moisture that is separated from the air stream by a moisture separator and removed by draining is the cheapest means of controlling a water problem. Sometimes a separator is combined in the same housing as a filter and is called a "filter" but not always. Other methods can be cobbled together to deal with a water problem. Of course there are always the more expensive commercial aftercoolers and driers that are available for a more complete "fix" if needed.

scott#2

scott#2